Radiological imaging apparatus and timing correction method therefor

ABSTRACT

A processing circuit, which carries out coincidence counting, acquires calibration data so that time delays of γ-ray detection signals from radiation detectors coincide with one another. A technique for acquiring calibration data faster and easily is provided to attain high time precision and respond to multi-channeling of detectors. A signal from a test signal generator is sent to signal processing apparatuses and coincidence count events are generated as a test. The events generated are processed by a delay time control apparatus and a variable delay circuit is controlled to improve the accuracy of coincidence counting.

CROSS REFERENCE TO RELATED APPLICATIONS

The application is a continuation of U.S. patent application Ser. No.11/174,589, filed on Jul. 6, 2005 now U.S. Pat. No. 7,129,476, thedisclosure of which is incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

The present invention relates to a radiological imaging apparatus and atiming correction method therefor, and more particularly, to aradiological imaging apparatus and a timing correction method thereforsuitable for use in a Positron Emission Tomography (hereinafter referredto as “PET”) apparatus.

A PET inspection is an inspection carried out by administering radiopharmaceuticals (hereinafter referred to as “PET pharmaceuticals”)containing positron emitters (¹⁵O, ¹³N, ¹¹C, ^(18F), etc.) and havingthe nature of accumulating in a specific region (e.g., cancer cells) toan examinee and detecting γ-rays emitted from the affected area of theexaminee by being provoked by the PET pharmaceuticals accumulated in theregion using radiation detectors. When a positron emitted from thepositron emitter contained in the PET pharmaceuticals encounters withneighboring electrons and annihilates, a pair of γ-rays having energy of511 keV are emitted in substantially diametrically opposite directions.It is possible to identify locations where the PET pharmaceuticals areaccumulated, that is, the affected area of cancer of the examinee basedon the respective detection signals outputted from a pair of radiationdetectors which have detected this pair of γ-rays.

To identify the affected area of cancer, it is necessary to identify therespective positions of the pairs of radiation detectors which havedetected the pairs of γ-rays generated by annihilation of positrons andit is necessary to take a coincidence count of detection signalsoutputted from these radiation detectors. This requires time resolutionwith high precision. However, even when γ-rays enter two radiationdetectors simultaneously, there is a variation in signal transmissionfrom the respective radiation detectors to a coincidence circuit andthere are differences in the times at which signals arrive at thecoincidence circuit. For this reason, it is necessary to adjusttransmission delays of signals from the respective radiation detectorsso that the times at which signals arrive at the coincidence circuitcoincide with one another.

Conventionally, timing correction of signals detected by radiationdetectors is realized by acquiring calibration data using a calibrationradiation source and adjusting a time variation of signal transmissionbased on the calibration data. This timing correction method isdescribed, for example, in JP-B-6-19436 and Japanese Patent No. 3343122.

The signal timing correction method described in JP-B-6-19436 will beexplained. First, γ-rays from the radiation source are detected by aradiation detector, a timing signal is created based on an output signalof the radiation detector and this timing signal is inputted to thecoincidence count apparatus through a delay adjusting circuit. Thesensitivity of the signal outputted from the coincidence count apparatusis measured. Next, the sensitivity of γ-rays from the radiation detectoris measured using the same method as that described above while changingan amount of delay to be set in the delay time adjusting circuit. Thisis the method of correcting a signal delay time by setting the amount ofdelay corresponding to the highest measured sensitivity in the delaytime control apparatus.

Next, the signal timing correction method described in Japanese PatentNo. 3343122 will be explained. This method corrects timings of signaltransmission by setting a calibration radiation source within a field ofview of the PET apparatus, creating timing data indicating a timedifference measured value of a coincidence event which occurs between apair of radiation detectors, calculating a time delay valuecorresponding to each radiation detector and setting this time delayvalue in the corresponding radiation detector channel.

However, the above described conventional technologies obtaincalibration data necessary for timing correction using a radiationsource and γ-rays emitted for one event form a pair, and therefore it ispossible to obtain calibration data for only the circuits connected tothe two radiation detectors into which the respective γ-rays areintroduced. For this reason, it takes a long time to obtain calibrationdata corresponding to all radiation detectors.

It is an object of the present invention to provide a radiologicalimaging apparatus and a timing correction method therefor capable ofreducing a time required to acquire timing calibration data to be usedfor timing correction of output signals of radiation detectors.

SUMMARY OF THE INVENTION

A feature of the present invention to attain the above described objectis to input a test signal outputted from a test signal generator to aplurality of signal processing apparatuses and generate timingcalibration data based on the outputs of the plurality of signalprocessing apparatuses. Since the present invention can input a testsignal to the respective signal processing apparatuses reliably, thetime required to acquire timing calibration data necessary for timingcorrection of output signals of the radiation detectors can be reduced.

It is preferable to carry out timing correction of γ-ray detectionsignals from the radiation detectors based on the calibration dataduring an inspection of an examinee.

According to the present invention, the time required to acquire timingcalibration data necessary for timing correction of output signals ofthe radiation detectors is shortened.

Other objects, features and advantages of the invention will becomeapparent from the following description of the embodiments of theinvention taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a PET apparatus which is an embodiment ofthe present invention;

FIG. 2 is a detailed block diagram of the signal processing unit shownin FIG. 1;

FIG. 3 is a block diagram of a PET apparatus which is another embodimentof the present invention;

FIG. 4 is a detailed block diagram of the signal processing unit shownin FIG. 3; and

FIG. 5 is block diagram of a signal processing unit of a PET apparatuswhich is a further embodiment of the present invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

With reference now to the attached drawings, embodiments will beexplained below.

Embodiment 1

A radiological imaging apparatus that is a preferred embodiment of thepresent invention will be explained below using FIG. 1 and FIG. 2. Theradiological imaging apparatus of this embodiment is a PET apparatus.

As shown in FIG. 1, the PET apparatus 40 of this embodiment is providedwith a bed 39 for holding an examinee (test subject), a plurality ofradiation detectors 1, a plurality of signal processing units 26, a timecorrection apparatus 10, a coincidence circuit 6, a delay time controlapparatus 7 and a test signal generator 15. The plurality of radiationdetectors 1 are arranged around the bed 39 in a ring shape surroundingthe bed 39. The radiation detectors 1 are also arranged in a pluralityof rows in the longitudinal direction of the bed 39. The radiationdetector 1 is a semiconductor radiation detector and approximately100,000 radiation detectors 1 are provided for the PET apparatus 40. Thesignal processing unit 26 which is provided for each radiation detector1 is provided with a signal processing apparatus 20 in the front stageand a packet data generator 28 in the posterior stage as shown in FIG.2. The signal processing apparatus 20 is provided with a preamplifier 2,and a timing signal generator 3 and a pulse height signal generator 11connected to the preamplifier 2. The preamplifier 2 is connected to theradiation detector 1. A switch (opening/closing device) 16 is connectedto the signal processing apparatus 20, that is, the preamplifier 2. Theswitch 16 is provided for each signal processing apparatus 20. All theswitches 16 are connected to the test signal generator 15. The packetdata generator 28 is provided with a time measuring apparatus 9 and apulse height measuring apparatus 12. The time measuring apparatus 9 isconnected to the timing signal generator 3. The pulse height measuringapparatus 12 is connected to the pulse height signal generator 11 on onehand and connected to the time measuring apparatus 9 on the other. Thetime measuring apparatus 9 is connected to the time correction apparatus10. The coincidence circuit 6 is connected to the time correctionapparatus 10. The delay time control apparatus 7 is connected to thecoincidence circuit 6 through a switch 21 and also connected to the timecorrection apparatus 10 through a switch 35. A data collection apparatus31 connected to the coincidence circuit 6 is connected to an imagereconstruction apparatus 33. A data saving apparatus 32 is connected tothe data collection apparatus 31. A display device 34 is connected tothe image reconstruction apparatus 33. In this embodiment, the delaytime control apparatus 7 is the calibration data generator whichgenerates calibration data.

For example, before starting a PET inspection everyday, it is possibleto acquire calibration data necessary for timing correction of the PETapparatus 40 using a test signal outputted from the test signalgenerator 15. The test signal is an electric signal, and morespecifically, a charge signal. It is difficult to send a charge signalfrom the test signal generator 15 to the preamplifier 2 and it isdesirable to convert a voltage signal to a charge signal through theswitch 16 or the preamplifier 2 using a capacitor. It is desirable torealize equi-length or equi-electric length wiring from the test signalgenerator 15 to the preamplifier 2, but it is also possible to obtain anamount of delay from the test signal generator 15 to the preamplifier 2through a calculation or comparison with measurement of the delay timeusing a radiation source to perform correction when creating calibrationdata. The method of acquiring calibration data in this embodiment willbe explained more specifically below. In this embodiment, calibrationdata is acquired using a test signal outputted from the test signalgenerator 15.

When acquiring the calibration data, the operator (radiologicaltechnician and medical doctor, etc.) operates buttons provided on anoperator console (not shown) whereby a data acquisition start signal isoutputted from the operator console to the test signal generator 15 anda switch control apparatus 18. Furthermore, this data acquisition startsignal is inputted to the delay time control apparatus 7 and all thecalibration data saved in the delay time control apparatus 7 whenprevious calibration data was acquired is thereby set to zero (or aspecific value). The test signal generator 15 generates a test signalthrough an input of the data acquisition start signal. This test signalis generated asynchronously to a measuring clock of a time counterinputted to the time measuring apparatus 9. Acquiring calibration datarequires the test signal to be inputted to each signal processingapparatus 20 connected to a pair of radiation detectors 1. The switchcontrol apparatus 18 starts a corresponding ON, OFF operation of theswitch 16 through the input of the data acquisition start signal. Thatis, the switch control apparatus 18 closes the two switches 16 connectedto the two signal processing apparatuses 20 together. Furthermore, theswitch control apparatus 18 also closes the switch 21. This switch 21remains closed during a calibration period. The test signal outputtedfrom the test signal generator 15 is inputted to the pair of signalprocessing apparatuses 20 through the respective switches 16. Wheninspecting the examinee, the signal processing apparatus 20 inputs aγ-ray detection signal outputted from the radiation detector 1 and whenacquiring calibration data, the signal processing apparatus 20 inputs atest signal through the switch 16.

Here, the opening/closing operation of the switch 16 will be explained.The opening/closing of the switch 16 is controlled by a command signalfrom the switch control apparatus 18. In this embodiment, in order toacquire calibration data, it is necessary to select a pair of signalprocessing apparatuses 20; a signal processing apparatus 20 which servesas a reference (hereinafter referred to as “reference signal processingapparatus”) and a signal processing apparatus 20 carrying outcalibration (hereinafter referred to as “calibration signal processingapparatus”) and input a test signal to each signal processing apparatus20. The test signal is preferably inputted to the pair of signalprocessing apparatuses 20 simultaneously. Pairs of reference signalprocessing apparatus 20 and calibration signal processing apparatus 20are preset and information on many combinations of reference signalprocessing apparatus 20 and calibration signal processing apparatus 20that form a pair is stored in a memory (not shown) of the switch controlapparatus 18. The reference signal processing apparatus 20 andcalibration signal processing apparatus 20 that form a pair correspondto a pair of signal processing apparatuses 20 connected to a pair ofradiation detectors 1 located in diametrically opposite directions whichdetect a pair of γ-rays during an inspection of the examinee. Othercombinations of reference signal processing apparatus 20 and calibrationsignal processing apparatus 20 are also stored in the above describedmemory. Some reference signal processing apparatuses 20 also serve ascalibration signal processing apparatuses 20. The switch controlapparatus 18 repeats “close (ON)” and “open (OFF)” operations of theswitch 16 connected to a certain reference signal processing apparatus20 based on the information on the combinations of the reference signalprocessing apparatus 20 and calibration signal processing apparatus 20stored in the memory until inputs of test signals to the referencesignal processing apparatus 20 and all calibration signal processingapparatuses 20 to be paired therewith are completed. Next, the switchcontrol apparatus 18 sequentially carries out “close” and “open”operations of the calibration signal processing apparatus 20 withrespect to the respective switches 16 connected to the reference signalprocessing apparatus 20. The test signal outputted from the test signalgenerator 15 is inputted to the calibration signal processing apparatus20 when the switch 16 is closed and the input of the test signal to thecalibration signal processing apparatus 20 is stopped when the switch 16is opened. That is, the test signal outputted from the test signalgenerator 15 is inputted to the pairs of reference signal processingapparatus 20 and calibration signal processing apparatus 20 sequentiallyand reliably. When inputs of a test signal to one reference signalprocessing apparatus 20 and all calibration signal processingapparatuses 20 to be paired therewith are completed, the switch controlapparatus 18 opens the switch 16 connected to the aforementionedreference signal processing apparatus 20 and stops the input of the testsignal. Then, the switch control apparatus 18 performs control ofturning ON/OFF the respective switches 16 connected to another referencesignal processing apparatus 20 and calibration signal processingapparatuses 20 paired therewith until the input of the test signal toall the reference signal processing apparatuses 20 is completed. This isthe opening/closing operation of the switch 16.

Next, the method of inputting a test signal to the reference signalprocessing apparatus 20 and calibration signal processing apparatus 20and acquiring calibration data using this test signal will be explainedmore specifically. For convenience, the time measuring apparatus 9connected to the reference signal processing apparatus 20 will be calleda “time measuring apparatus 9A” and the time measuring apparatus 9connected to the calibration signal processing apparatus 20 will becalled a “time measuring apparatus 9B.”

The test signal inputted to the reference signal processing apparatus 20is amplified by the preamplifier 2 and inputted to the timing signalgenerator 3. The timing signal generator 3 creates a timing signal basedon the test signal and outputs the timing signal to the time measuringapparatus 9A. The time measuring apparatus 9A measures the time at whichthe timing signal arrives and outputs time information (hereinafterreferred to as “first time information”). The time measuring apparatus9B outputs time information (hereinafter referred to as “second timeinformation”) based on the timing signal outputted from the timingsignal generator 3 of the calibration signal processing apparatus 20 towhich the test signal has been inputted. When the pulse height measuringapparatus 12 receives the time information from the time measuringapparatus 9, it obtains a detector ID to identify the radiation detector1 connected to the time measuring apparatus 9. That is, the pulse heightmeasuring apparatus 12 stores the detector ID corresponding to each timemeasuring apparatus 9 connected to the pulse height measuring apparatus12 and when time information is inputted from a certain time measuringapparatus 9, it is possible to identify the detector ID corresponding tothe time measuring apparatus 9. This is possible because the timemeasuring apparatus 9 is provided for each radiation detector 1. Whenthe first time information is inputted to the pulse height measuringapparatus 12, the pulse height measuring apparatus 12 identifies thecorresponding detector ID (detector ID of the radiation detector 1connected to the time measuring apparatus 9A, hereinafter referred to as“first detector ID”) and outputs it together with the first timeinformation. The pulse height measuring apparatus 12 identifies thecorresponding detector ID (detector ID of the radiation detector 1connected to the time measuring apparatus 9B, hereinafter referred to as“second detector ID”) based on the second time information and outputsit together with the second time information. The coincidence circuit 6receives the first time information, first detector ID, and second timeinformation and second detector ID outputted from the pulse heightmeasuring apparatus 12. The coincidence circuit 6 calculates a timedifference between the first time information which becomes a referencefor the pair of radiation detectors 1 and second time information(hereinafter referred to as “arrival time difference”). Even when a testsignal is inputted to the same reference signal processing apparatus 20and calibration signal processing apparatus 20, a variation occurs inthe time required for signal transmission, and therefore the test signalis inputted repeatedly to the same pair of signal processing apparatuses20 and the coincidence circuit 6 calculates the arrival time differencein each case. The delay time control apparatus 7 calculates an averageof the arrival time difference obtained from the coincidence circuit 6,calculates the calibration data to be set in all the radiation detectors1 mounted in the radiation detection apparatus based on the average andcauses the calibration data obtained to be stored in the memory of thedelay time control apparatus 7. Furthermore, the delay time controlapparatus 7 also stores the detector ID corresponding to the calibrationdata. The test signal is inputted to pairs of opposing signal processingapparatuses 20 until calibration data is created for all signalprocessing apparatuses 20. The calibration data for each signalprocessing apparatus 20 and the detector ID corresponding to thecalibration data are saved in the delay time control apparatus 7 andthis calibration data is used during a PET inspection of the examinee.After the acquisition of calibration data for all the signal processingapparatuses 20 is completed, the switch control apparatus 18 opens theswitch 21.

The test signal outputted from the test signal generator 15 is a signalhaving a sawtooth wave or square wave voltage signal. This test signalis converted to a pulse-shaped charge signal by a capacitor. To obtaintime information using the test signal, the amplitude of the waveformmay be constant, but by changing the amplitude of the signal waveform,it is possible to calibrate information other than time information, forexample, the relationship between the energy of γ-rays and the amplitudeof an electric signal outputted from the signal processing apparatus 20.

A CFD (Constant Fraction Discriminator) circuit or leading edge triggercircuit is used for the timing signal generator 3 provided for thesignal processing apparatus 20.

This embodiment, which uses a test signal from the test signalgenerator, can select a reference signal processing apparatus 20 andcalibration signal processing apparatus 20 reliably, and can therebyinput a test signal to a plurality of reference signal processingapparatuses 20 or a plurality of calibration signal processingapparatuses 20 reliably to acquire calibration data.

Next, the operation of the PET apparatus when carrying out a PETinspection of the examinee will be explained. During a PET inspection, atiming of a γ-ray detection signal is corrected using calibration dataobtained using a test signal.

Before starting a PET inspection, PET pharmaceuticals are administeredto the examinee by injection, etc., beforehand. The PET pharmaceuticalsare selected according to the purpose of the inspection. The PETpharmaceuticals administered to the examinee are concentrated on theaffected area of cancer of the examinee. The examinee administered thePET pharmaceuticals are laid on the bed 39.

When starting a PET inspection, the operator operates buttons providedon an operator console (not shown) and outputs an inspection startsignal to a centralized control section (not shown). When the inspectionstart signal is inputted, the centralized control section outputsinformation on the inspection target range of the examinee and a bedmovement start signal to a bed movement control section (not shown). Thebed movement control section, which has received the bed movement startsignal, moves the bed so that the inspection target range of theexaminee enters a γ-ray detection area of the PET apparatus 40 based onthe inputted information. The centralized control section, which hasreceived the inspection start signal, transfers the calibration datafrom the delay time control circuit 7 to the memory (not shown) of thetime correction apparatus 10. A PET inspection starts in this state.

Many pairs of γ-rays provoked by the PET pharmaceuticals are emitted inall directions from within the body of the examinee who lays on the bed39. A pair of γ-rays are emitted in substantially opposite directionsand detected by a pair of radiation detectors 1.

When these radiation detectors 1 detect γ-rays, they output pulse-likeelectric signals (hereinafter referred to as “γ-ray detection signals”)according to the energy of γ-rays. Since this γ-ray detection signal isfaint, the signal is amplified by the preamplifier 2 and inputted to thetiming signal generator 3. The timing signal generator 3 generates atiming signal indicating the time of detection of γ-rays based on theγ-ray detection signal and outputs the timing signal. The time measuringapparatus 9 calculates the arrival time of the timing signal and outputsthe time information obtained to the time correction apparatus 10through the pulse height measuring apparatus 12.

In this embodiment, the time correction apparatus 10 corrects theinputted time information with the calibration data, adjusts the delayin signal transmission and inputs the corrected time information to thecoincidence circuit 6. The method of correcting the time information(timing correction method) using the time correction apparatus 10 willbe explained below.

Time information corresponding to a γ-ray detection signal of theradiation detector 1 is inputted to the time correction apparatus 10together with a detector ID which identifies the radiation detector 1.As with the time of acquisition of calibration data, the detector ID isadded by the pulse height measuring apparatus 12. The time correctionapparatus 10 identifies the radiation detector 1 which outputted theγ-ray detection signal from which the inputted time information derivesusing the detector ID. The time correction apparatus 10 readscalibration data from the memory based on the detector ID. The timecorrection apparatus 10 corrects time information based on thecalibration data and outputs the corrected time information to thecoincidence circuit 6.

When the corrected time information signal is inputted to thecoincidence circuit 6, the coincidence circuit 6 decides based on thetime information whether the inputted signal is a γ-ray detection signalderived from a pair of γ-rays emitted from the affected area of theexaminee provoked by PET pharmaceuticals or not. The coincidence circuit6 compares time information of two signals out of the time informationcorresponding to γ-ray detection signals inputted successively andcalculates the time difference. The coincidence circuit 6coincidence-counts γ-ray detection signals corresponding to thecalculated time difference which falls within a set time (e.g., 10 nsec)(a pair of γ-ray detection signals produced by annihilation of onepositron). The coincidence circuit 6 outputs the detector IDs of therespective radiation detectors which have detected a pair ofcoincidence-counted γ-rays and information on the coincidence count tothe data collection apparatus 31.

The information inputted to the data collection apparatus 31 is saved inthe data saving apparatus 32 and after all measurements are completed,data is outputted to the image reconstruction apparatus 33. The imagereconstruction apparatus 33 creates information on the tomogramincluding the affected area of the examinee based on the information.The tomographic image is displayed on the display device 34.

This embodiment is intended to correct the difference in thetransmission time of γ-ray detection signals between detector channels(including the signal processing apparatuses 20) using the calibrationdata obtained using the aforementioned test signal.

This embodiment allows the following effects to be obtained.

(1) In this embodiment, a test signal outputted from the test signalgenerator 15 is inputted to the signal processing apparatus 20, andtherefore it is possible to input a test signal to all the signalprocessing apparatuses 20 reliably and acquire calibration data oftimings corresponding to detection signals of all the radiationdetectors included in the PET apparatus 40 in a short time. Especially,this embodiment inputs a test signal to the preamplifier 2, andtherefore it is possible to obtain more accurate calibration data whichreflects propagation times of a signal at the preamplifier 2 and timingsignal generator 3. It is also possible to obtain calibration data in ashorter time than the conventional example by connecting the test signalgenerator 15 between the preamplifier 2 and timing signal generator 3and inputting a test signal, which is an electric signal, to the timingsignal generator 3. However, in this case, the accuracy of calibrationdata is reduced compared to the case where a test signal is inputted tothe preamplifier 2 because the time for signal transmission at thepreamplifier 2 cannot be reflected. When a test signal is selectivelyinputted to the respective radiation detectors 1 using the test signalgenerator 15, it is necessary to use radiation or a very short lightpulse signal as the test signal. However, it is difficult to realize theinput of such a test signal to the radiation detector 1. Therefore, itis desirable to input the test signal to the signal processing apparatus20 without passing through the radiation detector 1.

(2) In this embodiment, the electric signal used as a test signal iseasier to handle than a radiation source used in the conventionalexample.

(3) In this embodiment, when calibration data is acquired, the switchcontrol apparatus 18 turns ON/OFF many switches 16 sequentially to inputa test signal to the corresponding pair of signal processing apparatuses20, and therefore it is possible to input the test signal to all thesignal processing apparatuses 20 reliably. Furthermore, compared to acase where the signal processing apparatus 20 is selected manually, itis possible to drastically reduce time and trouble.

In this embodiment, a test signal is inputted to a pair of signalprocessing apparatuses 20 respectively, but the number of signalprocessing apparatuses 20 to which a test signal is inputted is notalways 2 and it is possible to input a test signal to three or moresignal processing apparatuses 20 to acquire calibration data. That is,the switch control apparatus 18 turns ON, three or more, for example,ten switches 16 connected to ten signal processing apparatuses 20. Atest signal from the test signal generator 15 is inputted to the tencorresponding signal processing apparatuses 20. The coincidence circuit6 calculates an arrival time difference for each combination of two outof ten signal processing apparatuses 20. Information on combinations ofsignal processing apparatuses 20 for which an arrival time difference iscalculated is preset and stored in a memory (not shown) of thecoincidence circuit 6. Thus, by inputting a test signal to three or moresignal processing apparatuses 20 simultaneously, it is possible tofurther shorten the time required to acquire calibration datacorresponding to all radiation detectors 1.

(4) This embodiment outputs a test signal outputted from the test signalgenerator 15 asynchronously to the clock for measuring an arrival time.Such asynchronous outputting eliminates any correlation between apseudo-signal generation system and coincidence count system, and canthereby perform accurate calibration.

(5) This embodiment converts a signal detected by the radiation detector1 and a test signal from the test signal generator to digital values andprocesses the digitized time data. Using such a digital calculationfacilitates the setting of a time window. Furthermore, the digitalcircuit can be integrated more easily than a digital/analog circuit.

Embodiment 2

A radiological imaging apparatus which is another embodiment of thepresent invention will be explained using FIG. 3 and FIG. 4 below. Theradiological imaging apparatus of this embodiment is a PET apparatus.

The PET apparatus 40A of this embodiment has a configuration with thetime correction apparatus 10 in the PET apparatus 40 of Embodiment 1replaced by a variable delay circuit (delay adjustment apparatus) 4. ThePET apparatus 40A provides a signal processing unit 26A for eachradiation detector 1. The signal processing unit 26A is provided with asignal processing apparatus 20A which is the signal processing apparatus20 provided with the variable delay circuit 4. The variable delaycircuit 4 has its input end connected to a timing signal generator 3 andits output end connected to a coincidence circuit 6. A pulse heightmeasuring apparatus 12 is connected to a pulse height signal generator11 and the coincidence circuit 6. The rest of the structure of the PETapparatus 40A is the same as that of the PET apparatus 40.

When calibration data is acquired, a data acquisition start signal isinputted to a test signal generator 15 and a switch control apparatus 18as in the case of Embodiment 1. The switch control apparatus 18 closes apair of switches 16 connected to the corresponding pair of referencesignal processing apparatus 20 and calibration signal processingapparatus 20. A test signal outputted from the test signal generator 15is inputted to the reference signal processing apparatus 20 andcalibration signal processing apparatus 20 through the respectiveswitches 16.

The opening/closing operation of the switch 16 is the same as that ofEmbodiment 1, and therefore explanations thereof will be omitted.

A test signal inputted to the respective signal processing apparatuses20 is amplified by a preamplifier 2 and then inputted to the timingsignal generator 3. The timing signal generator 3 generates a timingsignal based on the test signal and outputs the timing signal to avariable delay circuit 4. When calibration data is acquired, a delaytime control apparatus 7 sets an amount of delay of the variable delaycircuit 4 (hereinafter referred to as “reference variable delay circuit4A”) connected to the reference signal processing apparatus 20 to aconstant value (e.g., a median value within the variable range).Furthermore, the amount of delay of the variable delay circuit 4(hereinafter referred to as “calibration variable delay circuit 4B”)connected to the calibration signal processing apparatus 20 is set to aminimum value. The variable delay circuit 4 delays and outputs thetiming signal based on the set amount of delay. The pulse heightmeasuring apparatus 12 calculates a pulse height based on the pulseheight signal outputted from the pulse height signal generator 11 andidentifies the corresponding detector ID. The coincidence circuit 6calculates sensitivity based on the delayed timing signal and pulseheight information. When the amount of delay set in the calibrationvariable delay circuit 4B is changed, the sensitivity to be calculatedby the coincidence circuit 6 also changes. The amount of delay time setin the calibration variable delay circuit 4B is gradually increased fromthe initially set value and the amount of delay time corresponding tothe maximum sensitivity is calculated. The information of the amount ofdelay corresponding to the maximum sensitivity is transmitted to thedelay time control apparatus 7 and stored in a memory (not shown) of thedelay time control apparatus 7. In this way, it is possible to obtaincalibration data corresponding to all signal processing apparatuses 20,and the calibration data and the corresponding detector IDs are storedin the memory of the delay time control apparatus 7.

The operation of the PET apparatus during a PET inspection of theexaminee will be explained using FIG. 3.

Differences from Embodiment 1 will be explained. When an inspectionstart signal is inputted to an overall control section (not shown), theoverall control section sends a delay amount setting signal to the delaytime control apparatus 7. The delay time control apparatus 7 which hasreceived the delay amount setting signal sends a command signal to thecorresponding variable delay circuit 4 so as to set the amount of delay(calibration data) to be set based on the detector ID (stored in thememory) of the radiation detector 1 connected to the variable delaycircuit 4. That is, before a PET inspection, the delay time controlapparatus 7 sets an amount of delay in all the variable delay circuits 4to obtain maximum sensitivity based on the calibration data saved in thememory. Furthermore, during a PET inspection, a switch 21 set betweenthe coincidence circuit 6 and the delay time control apparatus 7 isopened so that no γ-ray detection signal is inputted to the delay timecontrol apparatus 7.

A pair of γ-rays emitted from within the body of the examinee lying onthe bed 39 by being provoked by PET pharmaceuticals are detected by apair of radiation detectors 1. Based on the γ-ray detection signalsoutputted from the radiation detectors 1, the timing signal generated bythe timing signal generator 3 is inputted to the coincidence circuit 6through the corresponding variable delay circuit 4. That is, thevariable delay circuit 4 outputs the timing signal (time information)corrected based on the set amount of delay to the coincidence circuit 6.The coincidence circuit 6 carries out coincidence counting similar tothat in Embodiment 1 based on the timing signal. The coincidence circuit6 outputs detector IDs of the respective radiation detectors which havedetected a pair of coincidence-counted γ-rays and information on thecoincidence count value to a data collection apparatus 31.

The signal inputted to the data collection apparatus 31 is saved in adata saving apparatus 32 and data is outputted to an imagereconstruction apparatus 33 after all measurements are completed. Animage of the affected area of the examinee is created based on the dataprocessed by the image reconstruction apparatus 33 and the image isdisplayed on a display device 34.

A time window of the coincidence circuit 6 set when acquiringcalibration data of the PET apparatus 40A is preferably wider thanduring a PET inspection. Before calibration data is acquired, even if atest signal is inputted to the reference signal processing apparatus 20and calibration signal processing apparatus 20 simultaneously, thesignal arrives at the coincidence circuit 6 with a time variation. Whenthe time window of the coincidence circuit 6 is narrow, even the testsignals which have been inputted simultaneously may be processed asnon-coincidence signals by the coincidence circuit 6. For that reason,it is preferable to set a wide time window for the coincidence circuit 6when calibration data is acquired. In addition to the widening of theset value of the time window, it is possible to prevent a test signalfrom being processed as a non-coincidence signal by setting a timeperiod after a test signal is inputted to the calibration signalprocessing apparatus 20 until a test signal is inputted to the nextcalibration signal processing apparatus 20 to a value greater than acertain value.

This embodiment also inputs a test signal (electric signal) outputtedfrom the test signal generator 15 to the signal processing apparatus 20,and therefore it is possible to obtain the effects (1), (2) produced inEmbodiment 1.

Embodiment 3

A radiological imaging apparatus which is a further embodiment of thepresent invention will be explained using FIG. 5. The radiologicalimaging apparatus of this embodiment is a PET apparatus 40B anddifferent from the PET apparatus 40 in Embodiment 1 in that a pluralityof signal processing units 26B are provided. The structure of the PETapparatus 40B other than the signal processing unit 26B is the same asthat of the PET apparatus 40.

The signal processing unit 26B is provided with a signal amplifier 17, aplurality of analog ASICs 23, a plurality of digital ASICs 27 and a datamerge IC 25. Several tens of signal processing units 26B are arranged inthe PET apparatus 40B. 90 analog ASICs 23 are arranged for one signalprocessing unit 26B. Furthermore, a CFD (Constant FractionDiscriminator) circuit or leading edge trigger circuit is used for thetiming signal generator 3. The signal amplifier 17 is connected to atest signal generator 15. The analog ASIC 23 is provided with aplurality of signal processing apparatuses 20 and the same number ofswitches 16. Each signal processing apparatus 20 is provided with apreamplifier 2, and a timing signal generator 3 and a pulse heightsignal generator 11 connected to the preamplifier 2. The preamplifier 2is connected to a radiation detector 1. Each switch 16 provided for theanalog ASIC 23 is connected to the preamplifier 2 of each signalprocessing apparatus 20. These switches 16 are connected to the signalamplifier 17. In this embodiment, the signal amplifier 17 is connectedto the respective switches 16 of all the analog ASICs 23 provided withinthe signal processing unit 26B. The digital ASIC 27 includes a pluralityof packet data generators 28A and a data acquisition IC 24. The packetdata generator 28A is connected to each analog ASIC 23 and provided witha time measuring apparatus 9 which is individually connected to eachtiming signal generator 3 of one analog ASIC 23. The respective timemeasuring apparatuses 9 of the packet data generator 28A are connectedto one pulse height measuring apparatus 12. The pulse height measuringapparatus 12 is connected to each pulse height signal generator 11 ofone corresponding analog ASIC 23. The pulse height measuring apparatus12 of each packet data generator 28A is connected to the dataacquisition IC 24. The data integration IC 25 connected to a coincidencecircuit 6 is connected to the pulse height signal generator 11 of eachpacket data generator 28A.

The pulse height measuring apparatus 12 receives time information on thetime at which γ-rays are detected from the time measuring apparatus 9and identifies the detector ID. Furthermore, the pulse height measuringapparatus 12 measures pulse height information of a γ-ray detectionsignal proportional to the energy of γ-rays based on the output from thepulse height signal generator 11 connected to the pulse height measuringapparatus 12. The pulse height measuring apparatus 12 also functions asan information integration apparatus that integrates time information,detector ID information (detector position information) and pulse heightinformation. The information integration apparatus outputs theintegrated information (packet information) which is digital informationincluding those three types of information to the data acquisition IC24. The packet data (including time information, detector ID and pulseheight information) outputted from the pulse height measuring apparatus12 of each packet data generator 28A is outputted to the coincidencecircuit 6 (see FIG. 1) in the following stage through the data merge IC25.

This embodiment can obtain the effects (1) to (5) produced in Embodiment1 and can also obtain the following effects.

(6) Since this embodiment sets each switch 16 in the analog ASIC 23,wiring which transmits a test signal to the respective switches 16 canbe shared. For this reason, it is possible to drastically reduce thenumber of wires connecting the test signal generator 15 and therespective switches 16. Therefore, when the test signal generator 15 isprovided and wiring of the PET apparatus 40B is carried out, it ispossible to simplify the wiring work. The switches 16 are connected tothe respective signal processing apparatuses 20 included in the analogASIC 23, but it is also possible to achieve the same effect even if theswitches 16 are set between the signal processing apparatus 20 and timemeasuring apparatus 9.

It should be further understood by those skilled in the art thatalthough the foregoing description has been made on embodiments of theinvention, the invention is not limited thereto and various changes andmodifications may be made without departing from the spirit of theinvention and the scope of the appended claims.

The invention claimed is:
 1. A positron emission tomography, comprising:a plurality of radiation detectors arranged around a bed supporting anobject to be inspected; a plurality of signal processing apparatuseseach connected to each of said plurality of radiation detectors; a testsignal generator for outputting test signals to a plurality of saidsignal processing apparatuses; a plurality of gate apparatuses fortransferring said test signals, said gate apparatuses connected to saidtest signal generator and individually connected to a plurality of saidsignal processing apparatuses; a controller for controlling open andclose of a pair of said gate apparatuses on the basis of combinationinformation of a pair of said signal processing apparatuses, said gateapparatuses paired being connected to said signal processing apparatusespaired respectively, one of said signal processing apparatuses pairedbeing previously set as a reference and the other being previously setas a signal processing apparatus to be calibrated; a calibration datagenerator for generating timing calibration data for each of said signalprocessing apparatuses on the basis of outputs of said signal processingapparatuses paired, said outputs generated based on said test signalseach input to each of said signal processing apparatuses paired; andtiming correction means for correcting timings of radiation detectionsignals output from said radiation detectors on the basis of said timingcalibration data.
 2. A positron emission tomography according to claim1, wherein a plurality of said gate apparatuses are connected to saidtest signal generator using shared wiring.
 3. A positron emissiontomography according to claim 1, further comprising a coincidenceapparatus to which an output of said timing correction means is input.4. A positron emission tomography, comprising: a plurality of radiationdetectors arranged around a bed supporting an object to be inspected; aplurality of signal processing apparatuses each connected to each of aplurality of said radiation detectors; a test signal generator foroutputting test signals to a plurality of said signal processingapparatuses; a plurality of gate apparatuses for transferring said testsignals, said gate apparatuses connected to said test signal generatorand separately connected to a plurality of said signal processingapparatuses; a controller for controlling open and close of a pair ofsaid gate apparatuses on the basis of combination information of a pairof said signal processing apparatuses, said gate apparatuses pairedbeing connected to said signal processing apparatuses pairedrespectively, one of said signal processing apparatuses paired beingpreviously set as a reference and the other being previously set as asignal processing apparatus to be calibrated; a plurality of timegenerators each connected to each of a plurality of said signalprocessing apparatuses, each of said time generators generating timeinformation on the basis of an output of a corresponding one of saidsignal processing apparatuses; a calibration data generator forgenerating timing calibration data for each of a plurality of saidsignal processing apparatuses on the basis of outputs of said signalprocessing apparatuses paired, said outputs generated based on said testsignals each input to each of said signal processing apparatuses paired;and a time correction apparatus connected to a plurality of said timegenerators for correcting said time information output from said timegenerators on the basis of said timing calibration data.
 5. A positronemission tomography according to claim 4, further comprising acoincidence apparatus to which time information corrected by said timecorrection apparatus is input.
 6. A positron emission tomographyaccording to claim 4, wherein a plurality of said gate apparatuses areconnected to said test signal generator using shared wiring.
 7. Apositron emission tomography, comprising: a plurality of radiationdetectors arranged around a bed supporting an object to be inspected; aplurality of signal processing apparatuses each connected to each ofsaid plurality of radiation detectors; a test signal generator foroutputting test signals to a plurality of said signal processingapparatuses; a plurality of gate apparatuses for transferring said testsignals, said gate apparatuses connected to said test signal generatorand individually connected to a plurality of said signal processingapparatuses; a controller for controlling open and close of a pair ofsaid gate apparatuses on the basis of combination information of a pairof said signal processing apparatuses, said gate apparatuses pairedbeing connected to said signal processing apparatuses pairedrespectively, one of said signal processing apparatuses paired beingpreviously set as a reference and the other being previously set as asignal processing apparatus to be calibrated; a delay adjustmentapparatus connected to a plurality of said signal processing apparatusesindividually, for adjusting amounts of delay of outputs of said signalprocessing apparatuses; a calibration data generator for generatingtiming calibration data on the basis of outputs of said signalprocessing apparatuses paired, said outputs generated based on said testsignals each input to each of said signal processing apparatuses pairedand for adjusting an amount of delay of said delay adjustment apparatuson the basis of said timing calibration data.
 8. A positron emissiontomography according to claim 7, further comprising a coincidenceapparatus to which an output of said delay adjustment apparatus isinput.
 9. A positron emission tomography according to claim 7, wherein aplurality of said gate apparatuses are connected to said test signalgenerator using shared wiring.
 10. A method of correcting a timing in apositron emission tomography, comprising the steps of: previouslysetting a combination of a pair of signal processing apparatuses, one ofwhich is a signal processing apparatus as a reference and the other ofwhich is a signal processing apparatus to be calibrated; inputting testsignals generated from a test signal generator to said signal processingapparatuses paired respectively, via a pair of gate apparatuses closedby a controller, said signal processing apparatuses paired beingconnected to a pair of radiation detectors and said gate apparatusespaired; generating a timing calibration data on the basis of each outputof said signal processing apparatuses paired, said each output generatedbased on said test signals; and correcting timings of radiationdetection signals output from said radiation detectors on the basis ofsaid timing calibration data.
 11. A method of correcting a timing in apositron emission tomography according to claim 10, wherein said testsignals are electric signals.
 12. A method of correcting a timing in apositron emission tomography according to claim 11, wherein said testsignals are input to selected ones of a plurality of said signalprocessing apparatuses.
 13. A method of correcting a timing in apositron emission tomography according to claim 10, wherein said testsignals are input to selected ones of a plurality of said signalprocessing apparatuses.
 14. A method of correcting a timing in apositron emission tomography according to claim 13, wherein said testsignals are input to said signal processing apparatuses connected tosaid radiation detectors without passing through said radiationdetectors.
 15. A method of correcting a timing in a positron emissiontomography according to claim 10, wherein said test signals are input tosaid signal processing apparatuses connected to said radiation detectorswithout passing through said radiation detectors.
 16. A method ofcorrecting a timing in a positron emission tomography according to claim15, wherein said test signals are input to two or more of said signalprocessing apparatuses.
 17. A method of correcting a timing in apositron emission tomography according to claim 10, wherein said testsignals are input to two or more of said signal processing apparatuses.18. A method of correcting a timing in a positron emission tomographyaccording to claim 17, wherein said step of generating a timingcalibration data comprising the steps of: generating time information bya time generator on the basis of outputs of said signal processingapparatuses to which said test signals are input; and generatingcalibration data on the basis of said time information, wherein saidtest signals are asynchronously output with respect to measurementclocks input to said time generator for generation of said timeinformation.
 19. A method of correcting a timing in a positron emissiontomography according to claim 10, wherein said step of generating atiming calibration data comprising the steps of: generating timeinformation by a time generator on the basis of outputs of said signalprocessing apparatuses to which said test signals are input; andgenerating calibration data on the basis of said time information,wherein said test signals are asynchronously output with respect tomeasurement clocks input to said time generator for generation of saidtime information.